Hummingbird Heartbeat
by KookieEvans
Summary: In which Sam is shy, Dean is startled and Cas becomes a little more human. "There was definitely something weird happening to Sam Winchester." Castiel is determined to find out what. Slash.


**Disclaimer : I do not own anything recognisable at all, full kudos to those who do own it :)**

**Author's Note: Hey guys! This is my first ever, full on Sassy fanfiction. Wow. Scary stuff. I had planned on posting it on livejournal, but after getting confused by many attempts at using the lj cuts I gave up and came back to the comfort of . So yeah, that was a bit of a disappointment, I was hoping on getting out there a bit more, but I love more anyway :3 This whole story was inspired by a word from a thesaurus, but then I discovered the Katy Perry song of the same name, so check it out if you like her work. Anyway, enough rambling, I hope you like this!**

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><p>There was definitely something weird happening to Sam Winchester.<p>

Castiel probably should have noticed it earlier. On reflection it was painfully obvious that something was wrong with Sam. Whenever he appeared to the Winchesters he could sense it - Sam's heartbeat picked up very noticeably. The usually reassuring, steady throb stuttered and sped up every time Castiel was in the room, and honestly, the angel was starting to take it personally. Had he done something wrong? Human social interactions were very complicated.

"Sam," Castiel blinked into existence in front of the sofa occupied by the youngest Winchester, determined to find answers.

"Holy-!" Sam jumped in his seat, biting down to stop the curse that built up in his mouth from erupting. Immediately Castiel felt the human's pulse quicken, but had to admit it could be due to being startled by the sudden celestial appearance.

But when Castiel took a step towards the younger man, the loud thudding only became more rapid.

"Sam," Castiel repeated and frowned, a new theory presenting itself. "Are you afraid of me?"

"What? No," Sam chuckled. It was a nervous laugh, but Castiel could see no trace of a lie in the human's eyes. "Why, should I be?"

"No, I mean you no harm. At the moment."

Sam blinked, then shook his head, returning to the book he had been studying before he was interrupted.

"What was it you came here for anyway?" He asked. Castiel contemplated the situation, totally ignoring the question, and took a seat next to Sam. Sam's muscles stiffened and his eyes froze on a point in the dusty book's pages.

"If I do not scare you, then why does my presence make you uncomfortable?"

"I…don't know what you're talking about."

Castiel surveyed the man who was stubbornly avoiding eye contact, and decided the best way to prove his point would be with a practical demonstration. He slid along the sofa until the length of his leg was pressed firmly against Sam's. Sam gasped, the sharp inhale ringing out throughout the silent room.

"Do not lie to me, Sam," Castiel demanded, one eyebrow raised. Sam flicked through the pages of his book with shaking, panicked hands. Castiel caught Sam's chin gently and tilted his face so that they were looking at each other, only inches apart. He watched in fascination as the dark pupils of Sam's eyes dilated wildly. "I do not appreciate being ignored either."

Sam shivered under his hand, eyes darting between Castiel's eyes and lips, undecided. The angel wondered if he had something on his face. Castiel grew impatient and opened his mouth to speak, only to be silenced when nervous lips met his own.

Castiel realised that this was what humans called a kiss, and paid great attention to all of the details. It was his first kiss, and it would be nice to find out why humans seemed to enjoy the activity so greatly.

He had to admit, he could see the attraction. Sam's lips were much softer than he had imagined - this was also interesting, Castiel did not know when or why he had imagined the texture of Sam's lips before. Castiel let his eyes close softly, merely because it seemed like the right thing to do.

Something brushed his lips - Sam's tongue, he realised - and he shivered and stiffened at the feelings it evoked.

Like electric spikes of lightning to his brain, to his groin.

But too soon the lips were gone, and Castiel's eyes fluttered open, slightly stunned, nowhere near ready to lose the contact.

"Cas," Sam breathed softly and recoiled, cheeks pink and eyes mortified. "I'm so sorry! I shouldn't have-I…"

Sam trailed off, breath hitching and eyes darting around frantically. Castiel tried to speak, but couldn't seem to make any words. Sam hid under his fringe, ashamed, worrying his bottom lip between his teeth. Castiel lifted a curious finger to his own quivering lips and disappeared without a word.

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><p>In the weeks that followed, Castiel managed to avoid spending any time alone with Sam Winchester. He only appeared when he knew that Dean would be there, addressing only the eldest brother ad ignoring Sam, who suddenly became very interested in his research whenever the angel was around. Castiel knew he would have to talk to Sam at some point, but whenever he thought of that kiss his usually collected thought became…somewhat complicated.<p>

It didn't help that he felt different when he saw Sam now. He couldn't put his finger on it. It was like he didn't want to even glance in Sam's direction, but at the same time he wanted to stare and never look away.

The feelings only got worse when once, when he just happened to look over Sam accidentally caught his eye. The two men froze, not sure what to do. That's when he heard it. The sound of a heartbeat quickening.

But it wasn't Sam's.

Castiel stiffened further. His vessel's heart was fluttering like a hummingbird, pounding so loudly he wondered whether Sam, too, could hear it. As if that were not enough of a shock, Castiel's face suddenly heated up, and he realised he was _blushing. _

Since that day things had only gotten worse. He was confused, irritated and all he could think of was Sam. It was distracting more than anything, especially when he was trying to hold important conversations with Dean, while steadfastly ignoring the way Sam's shirt rode up to reveal a strip of skin when he stretched in the background.

Two weeks and four days after the kiss, Castiel snapped. He promised himself he would just try to talk with Sam about what had happened, and maybe the awkward thoughts would go away.

It had seemed like such a good idea at the time.

Castiel, determined, blinked into the Winchester's motel room.

And froze.

Sam stood beside a bed, wearing only a towel, with rivulets of water still streaming down his bare, blazing skin. Castiel sighed as he felt his resolve snap. He had tried, at least.

He crossed the room in the blink of an eye, shoving a startled Sam back against the wall roughly. Castiel curled his hands over Sam's hips, feelings the twitch of muscles beneath his fingers. He tilted his head upwards, clumsily seeking Sam's mouth with his own.

And then they were kissing, and it burned like fire on his lips, and he wondered if all humans kissed like this, or if it was just Sam. The damn abomination was far too good at kissing. A hand trailed over hot skin to tangle in still-wet hair.

Their clumsy, passionate kiss continued for what could have been forever, and when they eventually pulled apart, Castiel noticed that both of their hearts were beating ridiculously fast. Then again, he supposed he could put up with it as long as he and Sam could do this more often.

Sam grinned sheepishly down at him, and Castiel responded with a small, rare smile of his own.

"Whoa, wait, am I missing something here?" A familiar voice demanded attention. Castiel, in his…distracted state hadn't even noticed Dean had been in the room the whole time. Underneath him, Sam froze. "What the hell was that?"

Castiel just trailed his lips along Sam's neck, smiling still, taking in the taste of strong, clean skin. Yes, human social interactions were very complicated…

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><p><strong>Author's End Notes : <strong>**I really hope you liked it, please feel free to leave a review to tell me what you thought :)**


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